X-ray image acquisition apparatus

ABSTRACT

An X-ray image acquisition apparatus ( 15 ) includes a conversion panel ( 20 ) aligned with a photo detector array ( 40 ). The conversion panel ( 20 ) includes a plurality of conversion cells ( 22 ), each including a conversion body ( 31 ), an X-ray transparent and light reflective file over the top ( 32 ) of the body ( 31 ), and a light reflective film ( 36 ) surrounding the body ( 31 ). The body ( 31 ) is made of a scintillating material that efficiently generates optical light photons in response to X-ray radiation illuminating thereon and is substantially transparent to the optical light photons. The body ( 31 ) is also sufficiently long to absorb the X-ray radiation over a wide range of energy levels. The light reflective films ( 36, 38 ) collimate the optical light photons generated in the body ( 31 ) toward the photo detector array ( 40 ) to form X-ray images.

FIELD OF THE INVENTION

The present invention relates, in general, to image acquisition andspecifically to X-ray image acquisition.

BACKGROUNDS OF THE INVENTION

X-ray imaging is widely used in various fields of life. For example,X-ray imaging has been a standard medical diagnostic tool for decades. Atypical X-ray image acquisition apparatus suitable for low energy X-raysincludes a phosphor X-ray conversion screen and a photo detector arrayaligned with each other. The phosphor conversion screen generatesoptical light photons in response to the X-ray radiation. The opticallight photons are transmitted to the photo detector array under theconversion screen. The photo detector array generates electric signalsin response to the optical light photons. Electronics circuitry coupledto the photo detector array processes the electric signals and generateimages. A typical high energy X-ray image acquisition apparatus includesa copper screen and a Gadolinium Oxysulfide panel over a photo detectorarray. The high energy X-ray radiation passes through the copper screen,which absorbs a portion of the X-ray radiation and generates energeticelectrons. The electrons pass into the Gadolinium Oxysulfide panel andgenerate optical light photons. Another portion of the X-ray radiationpasses through the copper screen and interacts with GadoliniumOxysulfide to produce optical light photons. The photo detector arraysenses the optical light photons and generates electric signals inresponse thereto.

Different applications require images acquired using X-ray radiation atdifferent energy levels. For example in the field of medical diagnosticprocedures, low energy “diagnostic” X-ray images are generally used insoft tissue diagnostics, and high energy X-rays are used for treatmentin radiation oncology and imaging are produced with imaging systems inconjunction with the treatment. The quality of the acquired imagedepends on the image acquisition procedures and the equipment used.

X-ray images at different energy levels are presently created usingdifferent image acquisition apparatuses as described above. Maintainingmultiple sets of X-ray image apparatuses will increase the operating andoverhead costs for a medical diagnostic facility. It will also affectthe efficiency of the facility by increasing the idle time of theapparatuses. These effects are exacerbated further for those facilitieswith relatively small patient bases.

Accordingly, it would be advantageous to have an apparatus that iscapable of forming X-ray images with X-rays at different energy levels.It is desirable for the apparatus to be simple and reliable. It is alsodesirable if the apparatus can be used on an existing X-ray imagingsystem. It would be of further advantage to be able to optimize theimage quality for its intended use.

SUMMARY OF THE INVENTION

A primary benefit of the present invention is providing an apparatuscapable of forming X-ray images with X-rays at different energy levels.A particular benefit of some embodiments of the present invention isproviding the apparatus that is simple and reliable. A specific benefitof some embodiments of the present invention is providing the apparatusthat can be used on existing X-ray imaging systems. An additionalbenefit in accordance with some embodiments of the present invention isproviding the apparatus that is capable of optimizing the image qualityfor its intended use.

In order to achieve these and other objectives of the present invention,an X-ray image acquisition apparatus includes an X-ray conversion panelaligned with a photo detector array. The X-ray conversion panelgenerates optical light photons in response to the X-ray radiation ofdifferent energy levels. The photo detector array generates electricsignals in response to the optical light photon received from the X-rayconversion panel.

In accordance with an embodiment of the present invention, theconversion panel is made up of a plurality of X-ray conversion cellsarranged in a two-dimensional array. Each conversion cell has aconversion body in its core. The conversion body is made of ascintillating material, e.g., Cesium Iodine, Bismuth Germanate, CadmiumTungstate, etc., that generates optical light photons in response toX-ray radiation illuminating thereon and is substantially transparent tothe generated optical light photons. The conversion bodies arepreferably sufficiently long to absorb the X-ray radiation over a widerange of energy levels. Light reflective films are attached to thesidewalls of the conversion bodies to collimate the optical lightphotons generated in the conversion bodies. The cross section areas ofthe conversion bodies are preferably sufficiently small to provide asatisfactory spatial resolution of the X-ray image generated using theconversion panel. In a preferred embodiment, the top of each conversionbody is covered with an X-ray transparent and light reflective film.This film reflects those optical light photons generated in theconversion bodies and propagating away from the photo detector array,thereby increasing the efficiency of the conversion panel.

In accordance with an embodiment, the photo detector array includes anarray of photo detectors aligned with the conversion cells in theconversion panel and generating electric signals in response to theoptical light photons received from the corresponding conversion cellsin the conversion panel. Electronics circuits coupled to the photodetector array process the electric signals and generate the images.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an X-ray imaging system that includes an X-ray imageacquisition apparatus;

FIG. 2 illustrates a panel in the X-ray image acquisition apparatus ofFIG. 1;

FIG. 3 shows a cell in the panel of FIG. 2; and

FIG. 4 illustrate a photo detector array in the X-ray image acquisitionapparatus of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described hereinbelow with reference to the drawings. It should be noted that thedrawings are not to scale and elements of similar structures or similarfunctions are labeled with like reference numerals in the drawings.

FIG. 1 is a block diagram schematically illustrating an X-ray imagingsystem 10 in accordance with an embodiment of the present invention.X-ray imaging system 10 includes an X-ray radiation source 11 generatingX-ray radiation 12 and an X-ray image acquisition apparatus 15. Inaccordance with a preferred embodiment of the present invention,radiation source 11 is capable of generating X-ray radiation 12 atvarious energy levels. By way of example, radiation source 11 is able togenerate X-ray radiation 12 at a plurality of photon energy levelsranging between approximately 40 kilo-electron-volts (keV) toapproximately 20 mega-electron-volts (MeV). Radiation sources capable ofgenerating X-ray radiation at different energy levels are described inU.S. patent application Ser. No. 10/033,327 entitled “RADIOTHERAPYAPPARATUS EQUIPPED WITH AN ARTICULABLE GANTRY FOR POSITIONING AN IMAGINGUNIT” and filed on Nov. 2,2001, which is incorporated herein byreference in its entirety.

X-ray radiation 12 is used to form images an object 14 placed betweenradiation source 11 and X-ray image acquisition apparatus 15. The natureof object 14 depends on the application of X-ray imaging system 10. Forexample, in one application in accordance with the present invention,X-ray imaging system 10 is a piece of medical diagnostic equipment andobject 14 is a patient. In another application, X-ray imaging system 10is a structure inspection equipment and object 14 is a machine part tobe inspected. In yet another application in accordance with the presentinvention, X-ray imaging system 10 is a security or custom inspectionequipment and object 14 is a piece of luggage or cargo to be inspected.It should be understood that these examples are not meant to beexhaustive regarding the applications of X-ray imaging system 10.

X-ray image acquisition apparatus 15 includes an X-ray conversion panel20 and a photo detector array 40 suitably aligned with each other.During an imaging process, X-ray radiation 12 illuminates X-ray imageacquisition apparatus 15. As shown in FIG. 1, portions of X-rayradiation 12 reaches X-ray image acquisition apparatus 15 after passingthrough object 14. Because of their compositions and densities,different parts of object 14, e.g., different tissues in the body of apatient, may attenuate X-ray radiation 12 differently. For example, thebones in a patient generally attenuate X-ray radiation 12 moresignificantly than the soft tissues. In response to X-ray radiation 12illuminating thereon, X-ray image acquisition apparatus 15 generateselectric signals. Electronic circuits 16 coupled to x-ray imageacquisition apparatus 15 processes the electric signals and generatesthe X-ray images of object 14 at a display device 18.

FIG. 2 schematically shows X-ray conversion panel 20 in X-ray imageacquisition apparatus 15 in accordance with an embodiment of the presentinvention. Panel 20 includes a plurality of cells 22. In one embodiment,cells 22 are arranged in a two-dimensional array a plurality of rows anda plurality of columns. Cells 22, which are also referred to as X-rayconversion cells or conversion cells, are configured to generate opticallight photons in response to X-ray radiation 12 shown in FIG. 1. Inaccordance with one embodiment, adhesive is used to form conversionpanel 20 from X-ray conversion cells 22. In accordance with anotherembodiment, a grid (not shown) is used to arrange conversion cells 22into the two-dimensional array of X-ray conversion panel 20. Other meanscan also be used to form the array of X-ray conversion panel 20 usingconversion cells 22.

FIG. 3 is a schematic cross sectional view of an X-ray conversion cell30 in accordance with an embodiment of the present invention. Cell 30can be any of conversion cells 22 that form X-ray conversion panel 20shown in FIG. 2. Conversion cell 30 includes an X-ray conversion body 31having first end 32, a second end 33, and a sidewall 34 extending atleast partially between first end 32 and second end 33. In accordancewith one embodiment, conversion body 31 is a rod, in which first end 32and second end 33 are a top and a bottom, respectively, of rod 31.Conversion body 31 also has a sidewall 34 between first end 32 andsecond end 33. In accordance with the present invention, conversion body31 is made of a material that generates optical light photons inresponse to X-ray radiation.

Preferably, conversion body 31 is capable of absorbing the X-rayradiation at various energy levels. In accordance with an embodiment ofthe present invention, conversion cell 31 is able to generate theoptical light photons having a spectrum ranging between infrared andultraviolet in response to the X-ray radiation having photon energylevels ranging between approximately 40 kilo-electron-volts (keV) and 20mega-electron-volts (MeV). These characteristics are achieved byselecting a suitable material and an appropriate length or height forconversion body 31. In accordance with an embodiment of the presentinvention, the material has a high X-ray radiation absorption efficiencyand is substantially transparent to the optical light photons. Preferredmaterials for conversion body 31 include Cesium Iodine, BismuthGermanate, Cadmium Tungstate, etc. Generally, the longer conversion cell31, the more X-ray radiation it can absorb. Preferably, conversion cell31 has an optimum length or height depending on X-ray absorptionefficiency, image resolution, light collection efficiency, and otherparameters of the X-ray imaging system design. By way of example,conversion cell 31 has a length or height of at least 0.5 centimeter. Inone embodiment, conversion cell 31 has a length or height ofapproximately one centimeter. Conversion cell 31 can also have a lengthgreater than one centimeter. As shown in FIGS. 2 and 3, the length orheight of conversion cell 31 substantially determines the thickness ofconversion panel 20.

In one embodiment, first end 32 and second end 33 of conversion body 31have substantially the same geometric shape and size, and aresubstantially parallel to each other. In addition in the embodiment,sidewall 34 of conversion body 31 is substantially perpendicular tofirst end 32 and second end 33. In an embodiment optimized for spatialresolution, conversion bodies 31 in conversion panel 20 are configuredto point to a spot, from which X-ray radiation source 11 emits X-rayradiation 12. Preferred geometric shapes for first end 32 includesquare, rectangle, hexagon, etc. The size of first end 32 determines thespatial resolution of the images formed using conversion panel 20. Inaccordance with a an embodiment, first end 32 of conversion body 31 is asquare having a side ranging between approximately 0.1 millimeter andapproximately 0.5 millimeter. In accordance with a specific embodiment,the side of square shaped first end 32 of conversion body 31 is 0.388millimeter, which matches the photo diode pitch in photo detector array40.

Conversion cell 30 further includes a light reflective film 36 attachedto sidewall 34 of conversion body 31. Film 36 surrounds conversion body31 and reflects those optical light photons propagating toward sidewall34 back to the interior of conversion body 31. Therefore, film 36 servesto collimate and reflect the optical light photons generated inconversion body 31. In a specific embodiment, conversion cell 30 alsoincludes an X-ray transparent and light reflective film 38 attached tofirst end 32 of conversion body 31. Film 38 reflects those optical lightphotons propagating toward first end 32 back toward second end 33 ofconversion body 31, thereby increasing the intensity of the lightreaching photo detector array 40 under conversion panel 20 in X-rayimage acquisition apparatus 15 as shown in FIG. 1. In one embodiment,film 38 on first end 32 of conversion body 31 is a portion of an X-raytransparent and light reflective film covering the entire first end ofconversion panel 20 shown in FIG. 2. The film covers the first ends ofall conversion cells 22 in X-ray conversion panel 20. In anotherembodiment, film 38 is integrally formed with film 36 attached tosidewall 34 of conversion body 31. In this embodiment, film 36 and film38 form a light reflective pocket, in which conversion body 31 ispositioned. In yet another embodiment, film 36 for different conversioncells 22 in conversion panel 20 form a grid and conversion cells 22 arepositioned in the grid, thereby forming the two-dimensional array ofconversion cells in conversion panel 20. Film 36 and film 38 can be madeof light reflective materials commercially available. For example, apowder of small grain Magnesium Oxide supported by an appropriateadhesive is a suitable material for light reflective film 36 and film38. It should be understood that the proper operation of X-ray imageacquisition apparatus 15 requires film 38 attached to first end 32 ofconversion body 31 to be transparent to the X-ray radiation. On theother hand, whether film 36 attached to sidewall 34 of conversion body31 is transparent to the X-ray radiation does not significantly affectthe operation of X-ray image acquisition apparatus 15.

FIG. 4 is a top view of photo detector array 40 in X-ray imageacquisition apparatus 15 in accordance with an embodiment of the presentinvention. Photo detector array 40 includes a plurality of photodetectors 42 arranged in a two-dimensional array. Photo detectors 42 areconfigured to generate electric signals in response to the optical lightphotons illuminating thereon. In a specific embodiment, photo detectors42 are amorphous silicon photo detectors. Each of photo detectors 42forms a pixel of the X-ray image generated using photo detector array40. Photo detector array 40 also includes a pixel access circuit 54coupled to photo detectors 42. Pixel access circuit 54 accesses photodetectors 42 and reads the electric signals from photo detectors 42. Theprocess of accessing photo detectors 42 and reading electric signalstherefrom is known to those skilled in the art. In accordance with aspecific embodiment, pixel access circuit 54 generates row accesssignals to sequentially access photo detectors 42 by rows and readselectric signals out of photo detectors 42 by columns. Each row accesssignal can access either a single row or a plurality of rows of photodetectors 42. Likewise, each read action can read electric signals fromeither a single column or a plurality of columns of photo detectors 42.

The size of each photo detector 42, which is also referred to as a pixelsize, determines the spatial resolution of the X-ray images generatedusing photo detector array 40. Smaller pixel size results in betterspatial resolution. Accessing more than one row and reading electricsignals from more than one column during each read action increases thereading speed, but it will result in lower spatial resolution.

Preferably, photo detectors 42 in photo detector array 40 are alignedwith X-ray conversion cells 22 in X-ray conversion panel 20. In oneembodiment, each conversion cell 22 in conversion panel 20 is alignedwith one photo detector 42 in photo detector array 40. In thisembodiment, the size of conversion cells 22 is about the same as that ofphoto detectors 42. The maximum spatial resolution of the X-ray imagesgenerated using X-ray image acquisition apparatus 15 is equal to thepixel size of photo detectors 42 in photo detector array 40. In analternative embodiment, conversion cells 22 in X-ray conversion panel 20are larger than photo detectors 42 in photo detector array 40 and eachconversion cell 22 is aligned with more than one photo detectors 42. Inthis embodiment, the maximum spatial resolution of the X-ray images isdetermined by the size of conversion cells 22.

FIG. 4 shows pixel access circuit 54 located on the side of photodetectors 42. This arrangement keeps pixel access circuit 54 out of thepropagation paths of X-ray radiation 12 from X-ray source 11 and theoptical light photons generated in conversion panel 20, therebybenefiting the lifetime of pixel access circuit 54. However, the presentinvention is not limited to such an arrangement. In an alternativeembodiment, photo detectors 42 are mounted on one side of a substrateand pixel access circuit 54 is located on the other side of thesubstrate. The substrate protects pixel access circuit 54 from possibledamage caused by the X-ray radiation and the optical light photonillumination. This arrangement reduces the physical size of photodetector array 40 without reducing the number of pixels therein.

By now it should be appreciated that an X-ray image acquisitionapparatus capable of forming images of X-rays at different energy levelshas been provided. The X-ray image acquisition apparatus in accordancewith the present invention includes an X-ray conversion panel alignedwith a photo detector array. The X-ray conversion panel is configured togenerate optical light photons in response to the X-ray radiation. Theconversion panel includes a plurality of conversion cells, eachincluding a conversion body in its core and a light reflective filmsurrounding the body. The conversion body is made of a material thatefficiently generates optical light photons in response to X-rayradiation illuminating thereon and is substantially transparent to theoptical light photons. The conversion bodies are preferably sufficientlylong to absorb the X-ray radiation over a wide range of energy levels.The light reflective films collimate the optical light photons generatedin the conversion bodies. In a preferred embodiment, the first ends ofconversion bodies are covered with an X-ray transparent and lightreflective film to increase the efficiency of the conversion panel. Thephoto detector array aligned with the conversion panel is configured togenerate electric signals in response to the optical light photonsreceived from the conversion panel. Electronic circuits coupled to thephoto detector array process the electric signals and generate theimages.

While preferred embodiments of the present invention have been describedwith reference to the drawings, these are not intended to limit thescope of the present invention, which is set forth in the appendingclaims. Various modifications of the above described embodiments can bemade by those skilled in the art after browsing the specification of thesubject application. These modifications are within the scope and truespirit of the present invention. For example, the photo detector arrayin the X-ray image acquisition apparatus can be replaced with aphotographic film that is sensitive to the optical light photonsgenerated in the X-ray conversion panel in accordance with the presentinvention. Further, the X-ray image acquisition apparatus is not limitedto being used on an imaging system with an X-ray radiation sourcecapable of generating X-rays at different energy levels. The X-ray imageacquisition apparatus of the present invention can be used on differentimaging systems, each system including an X-ray radiation source that iscapable of generating X-ray radiation either at a single energy level orat multiple energy levels.

What is claimed is:
 1. An X-ray image acquisition apparatus, comprisinga panel having a plurality of cells, each of said plurality of cellscapable of generating optical light photons in response to X-rayradiation at a first energy level and a second energy level, each of thefirst and the second energy levels being a value that is betweenapproximately 40 kilo-electron-volts and approximately20-mega-electron-volts, the first energy level being in akilo-electron-volt range, the second energy level being in amega-electron-volt range, each of said plurality of cells including abody made of a scintillating material, said body having a first end, asecond end, and a sidewall extending at least partially between thefirst end and the second end.
 2. The X-ray image acquisition apparatusof claim 1, each of said plurality of cells in said panel furtherincluding a light reflective film attached to the side wall of said bodyand an X-ray transparent and light reflective film attached to the firstend of said body.
 3. The X-ray image acquisition apparatus of claim 1,said plurality of cells in said panel being focused to a radiationemitting point of an X-ray radiation source.
 4. The X-ray imageacquisition apparatus of claim 1, the first end of said body in each ofsaid plurality of cells in said panel being substantially a squarehaving a side between approximately 0.05 millimeter and approximately0.5 millimeter.
 5. The X-ray image acquisition apparatus of claim 1,said body in each of said plurality of cells in said panel having alength of approximately one centimeter.
 6. The X-ray image acquisitionapparatus of claim 1, said body in each of said plurality of cells insaid panel being made of the scintillating material that significantlyabsorbs the X-ray radiation at the plurality of photon energy levels,each of said plurality of photon energy levels being a value that isbetween approximately 40 kilo-electron-volts and approximately20-mega-electron-volts, and wherein the scintillating material issubstantially transparent to the optical light photons.
 7. The X-rayimage acquisition apparatus of claim 6, said body being made of CesiumIodine.
 8. The X-ray image acquisition apparatus of claim 6, said bodybeing made of Bismuth Germanate.
 9. The X-ray image acquisitionapparatus of claim 6, said body being made of Cadmium Tungstate.
 10. TheX-ray image acquisition apparatus of claim 1, further comprising a photodetector array aligned with said panel.
 11. An X-ray image acquisitionapparatus, comprising: a conversion panel configured to absorb X-rayradiation at a first energy level and a second energy level, each of thefirst and the second energy levels being a value that is betweenapproximately 40 kilo-electron-volts and approximately 20mega-electron-volts, the first energy level being in akilo-electron-volt range, the second energy level being in amega-electron-volt range, and conversion panel further configured togenerate optical light photons having a spectrum range between infraredand ultraviolet in response thereto; and a photo detector array alignedwith said conversion panel and configured to generate electric signalsin response to the optical light photons received from said conversionpanel.
 12. The X-ray image acquisition apparatus of claim 11, whereinsaid conversion panel includes: a plurality of conversion bodies made ofa scintillating material that generates the optical light photons inresponse to the X-ray radiation, said plurality of conversion bodiesbeing substantially transparent to the optical light photons and havinga plurality of first ends aligned with each other, a plurality of secondends aligned with each other, and a plurality of sidewalls extending atleast partially between the plurality of first ends and the plurality ofsecond ends; and a plurality of light reflective films attached to theplurality of sidewalls of said plurality of conversion bodies.
 13. TheX-ray image acquisition apparatus of claim 12, wherein said conversionpanel further includes an X-ray transparent and light reflective filmcovering the plurality of first ends of said plurality of conversionbodies.
 14. The X-ray image acquisition apparatus of claim 12, whereineach of said plurality of conversion bodies has a height sufficient tosubstantially absorb the X-ray radiation at the first and second energylevels.
 15. The X-ray image acquisition apparatus of claim 14, whereinthe height of each of said plurality of conversion bodies is at least0.5 centimeter.
 16. The X-ray image acquisition apparatus of claim 12,wherein said plurality of conversion bodies are made of thescintillating material selected from the group consisting of CesiumIodine, Bismuth Germanate, and Cadmium Tungstate.
 17. The X-ray imageacquisition apparatus of claim 12, wherein said photo detector arrayincludes a plurality of amorphous silicon detectors, each having a photodiode pitch.
 18. The X-ray image acquisition apparatus of claim 17,wherein the second end of each of said plurality of conversion bodies issubstantially a square having a side matching the photo diode pitch. 19.An X-ray image acquisition apparatus, comprising: a conversion panelcomprised of a plurality of cells, each of said plurality of cellsincluding: a body having a top, a bottom, and a sidewall between the topand the bottom, said body capable of generating optical light photons inresponse to X-ray radiation at a plurality of photon energy levels, eachof said plurality of photon energy levels being a value that is betweenapproximately 40 kilo-electron-volts to approximately 20mega-electron-volts, wherein one of said plurality of photon energylevel is in a kilo-electron-volt range, and another of said plurality ofphoton energy level is in a mega-electron-volt range; a light reflectivefilm surrounding the sidewall of said body; and an X-ray transparent andlight reflective film covering the top of said body; and a photodetector array aligned with said conversion panel and including aplurality of amorphous silicon detectors.
 20. The X-ray imageacquisition apparatus of claim 19, wherein said body in each of saidplurality of conversions cell in said conversion panel has a length ofat least one centimeter, and is aligned with at least one of saidplurality of amorphous silicon detectors in said photo detector array.